Recent work has shown that modifications of general relativity based on the addition to the action of a nonlocal term $R{\square }^{-2}R$, or on the addition to the equations of motion of a term involving $(g_{\mu \nu }{\square }^{-1}R)$, produce dynamical models of dark energy which are cosmologically viable both at the background level and at the level of cosmological perturbations. We explore a more general class of models based on the addition to the action of terms proportional to $R_{\mu \nu }{\square }^{-2}{R}^{\mu \nu }$ and $C_{\mu \nu \rho \sigma }{\square }^{-2}{C}^{\mu \nu \rho \sigma }$, where $C_{\mu \nu \rho \sigma }$ is the Weyl tensor. We find that the term $R_{\mu \nu }{\square }^{-2}{R}^{\mu \nu }$ does not give a viable background evolution. The nonlocal Weyl-square term, in contrast, does not contribute to the background evolution but we find that, at the level of cosmological perturbations, it gives instabilities in the tensor sector. Thus, only nonlocal terms which depend just on the Ricci scalar $R$ appear to be cosmologically viable. We discuss how these results can provide a hint for the mechanism that might generate these effective nonlocal terms from a fundamental local theory.

Arm locking is a technique for stabilizing the frequency of a laser in an interspacecraft interferometer by using the spacecraft separation as the frequency reference. A candidate technique for future space-based gravitational wave detectors such as the Laser Interferometer Space Antenna, arm locking has been extensive studied in this context through analytic models, time-domain simulations, and hardware-in-the-loop laboratory demonstrations. In this paper we show the laser ranging interferometer instrument flying aboard the upcoming Gravity Recovery and Climate Experiment follow-on (GRACE-FO) mission provides an appropriate platform for an on-orbit demonstration of the arm-locking technique. We describe an arm-locking controller design for the GRACE-FO system and a series of time-domain simulations that demonstrate its feasibility. We conclude that it is possible to achieve laser frequency noise suppression of roughly 2 orders of magnitude around a Fourier frequency of 1 Hz with conservative margins on the system’s stability. We further demonstrate that “pulling” of the master laser frequency due to fluctuating Doppler shifts and lock acquisition transients is less than 100 MHz over several GRACE-FO orbits. These findings motivate further study of the implementation of such a demonstration.

We show that the integration-by-parts reductions of various two-loop integral topologies can be efficiently obtained by applying unitarity cuts to a specific set of subgraphs and solving associated polynomial (syzygy) equations.

For supersymmetric extensions of the Standard Model with light sgoldstinos—scalar and pseudoscalar superpartners of goldstinos—we estimate the signal rate anticipated at the recently proposed fixed target experiment SHiP utilizing a CERN Super Proton Synchrotron beam of 400 GeV protons. We also place new limits on the model parameters from a similar analysis of the published results of the CHARM experiment.

The location of the critical end point of QCD has been determined in previous studies of $N_f=2+1$ and $N_f=2+1+1$ dynamical quark flavors using a (truncated) set of Dyson-Schwinger equations for the quark and gluon propagators of Landau-gauge QCD. A source for systematic errors in these calculations has been the omission of terms in the quark-gluon interaction that can be parametrized in terms of baryonic degrees of freedom. These have a potentially large dependence on chemical potential and therefore may affect the location of the critical end point. In this exploratory study we estimate the effects of these contributions, both in the vacuum and at finite temperature and chemical potential. We find only a small influence of baryonic contributions on the location of the critical end point. We estimate the robustness of this result by parameterizing further dependencies on chemical potential.

The long-range electromagnetic interaction presents a challenge for numerical computations in $\mathrm{QCD}+\mathrm{QED}$. In addition to power-law finite volume effects, the standard lattice gauge theory approach introduces nonlocality through removal of photon zero-momentum modes. The resulting finite volume effects must be quantitatively understood; and, to this end, nonrelativistic effective field theories are an efficient tool, especially in the case of composite particles. Recently an oddity related to nonlocality of the standard lattice approach was uncovered by the Budapest-Marseille-Wuppertal collaboration. Explicit contributions from antiparticles appear to be required so that finite volume QED results for a pointlike fermion can be reproduced in the effective field theory description. We provide transparency for this argument by considering pointlike scalars and spinors in finite volume QED using the method of regions. For the more germane case of composite particles, we determine that antiparticle modes contribute to the finite volume electromagnetic mass of composite spinors through terms proportional to the squares of timelike form factors evaluated at threshold. We extend existing finite volume calculations to one order higher, which is particularly relevant for the electromagnetic mass of light nuclei. Additionally, we verify that the analogous finite volume contributions to the nucleon mass in chiral perturbation theory vanish in accordance with locality.

We calculate the next-to-next-to-leading correction to the expectation value of the Polyakov loop or equivalently to the free energy of a static charge. This correction is of order $g^5$. We show that up to this order the free energy of the static charge is proportional to the quadratic Casimir operator of the corresponding representation. We also compare our perturbative result with the most recent lattice results in SU(3) gauge theory.

We describe in detail a previously published measurement of $CP$ violation in $B^0$-${\overline{B}}^0$ oscillations, based on an integrated luminosity of $425.7{\mathrm{fb}}^{-1}$ collected by the BABAR experiment at the PEPII collider. We apply a novel technique to a sample of about 6 million ${\overline{B}}^0\to D^{*+}{\ell }^{-}\overline{{\nu }_{\ell }}$ decays selected with partial reconstruction of the $D^{*+}$ meson. The charged lepton identifies the flavor of one $B$ meson at its decay time, the flavor of the other $B$ is determined by kaon tagging. We determine a $CP$ violating asymmetry ${\mathcal{A}}_{CP}=(N(B^0{B}^0)-N({\overline{B}}^0{\overline{B}}^0))/(N(B^0{B}^0)+N({\overline{B}}^0{\overline{B}}^0))=(0.06\pm 0.17_{-0.32}^{+0.38})\%$ corresponding to ${\mathrm{\Delta }}_{CP}=1-|q/p|=(0.29\pm 0.84_{-1.61}^{+1.88})\times 10^{-3}$. This measurement is consistent and competitive with those obtained at the $B$ factories with dilepton events.

We numerically study the head-on scattering of a ’t Hooft-Polyakov magnetic monopole and antimonopole for a wide range of parameters. In contrast to the scattering of a $\lambda {\varphi }^4$ kink and antikink in $1+1$ dimensions, we find that the monopole and antimonopole annihilate even when scattered at relativistic velocities. If the monopole and antimonopole have a relative twist, there is a repulsive force between them and they can initially be reflected. However, in every case we have examined, the reflected monopoles remain bound and eventually annihilate. We also calculate the magnetic helicity in the aftermath of monopole-antimonopole annihilation and confirm the conversion of relative twist to magnetic helicity as discussed earlier in the electroweak case.

The ATLAS Collaboration has reported excesses in the search for resonant diboson production with decay modes to hadronic final states at a diboson invariant mass around 2 TeV in boosted jets from $WZ$, $W^{+}{W}^{-}$, and $ZZ$ channels. Given potential contamination, we investigate the anomalies in leptophobic $U(1{)}_{\mathrm{LP}}$ models. We show that leptophobic models can be constructed in flipped $SU(5)\times U(1{)}_X$ models from free fermionic string constructions and Pati-Salam models from D-brane constructions. Additionally, we perform a collider phenomenological analysis to study production cross sections for $pp\to Z^{\prime }\to jj/t\overline{t}/WW/Zh$ and discover the excess can be interpreted in both the leptophobic flipped $SU(5)\times U(1{)}_X$ models and intersecting D-branes.

In this paper, the two-point function of linearized gravitons on de Sitter (dS) space is presented. Technically, respecting the dS ambient space notation, the field equation is given by the coordinate-independent Casimir operators of the de Sitter group. Analogous to the quantization of the electromagnetic field in Minkowski space, the field equation admits gauge solutions. The notation allows us to exhibit the formalism of Gupta-Bleuler triplets for the present field in exactly the same manner as it occurs for the electromagnetic field. In this regard, centering on the spin-two part (the traceless part, ${\mathcal{K}}^t$), the field solution is written as a product of a generalized polarization tensor and a minimally coupled massless scalar field. Then, admitting a de Sitter–invariant vacuum through the so-called “Krein space quantization,” the de Sitter fully covariant two-point function is calculated. This function is interestingly free of pathological large distance behavior (infrared divergence). Moreover, the spin-zero part (the pure-trace part; ${\mathcal{K}}^{pt}$) of the field is discussed in this paper. It is shown that the implications of the dS group unitary irreducible representations restrict the gauge-fixing parameter to the optimal value, which remarkably results in the pure-trace part be written in terms of a conformally coupled massless scalar field.

We present a new computation of the asymptotic gravitational wave energy fluxes emitted by a spinning particle in circular equatorial orbits about a Kerr black hole. The particle dynamics is computed in the pole-dipole approximation, solving the Mathisson-Papapetrou equations with the Tulczyjew spin-supplementary-condition. The fluxes are computed, for the first time, by solving the $2+1$ Teukolsky equation in the time-domain using hyperboloidal and horizon-penetrating coordinates. Denoting by $M$ the black hole mass and by $\mu$ the particle mass, we cover dimensionless background spins $a/M=(0,\pm 0.9)$ and dimensionless particle spins $-0.9\le S/{\mu }^2\le +0.9$. Our results span orbits of Boyer-Lindquist coordinate radii $4\le r/M\le 30$; notably, we investigate the strong-field regime, in some cases even beyond the last-stable-orbit. We compare our numerical results for the gravitational wave fluxes with the 2.5th order accurate post-Newtonian (PN) prediction obtained analytically by Tanaka et al. [Phys. Rev. D 54, 3762 (1996)]: we find an unambiguous trend of the PN-prediction toward the numerical results when $r$ is large. At $r/M=30$ the fractional agreement between the full numerical flux, approximated as the sum over the modes $m=1$, 2, 3, and the PN prediction is $\lesssim 0.5\%$ in all cases tested. This is close to our fractional numerical accuracy ($\sim 0.2\%$). For smaller radii, the agreement between the 2.5PN prediction and the numerical result progressively deteriorates, as expected. Our numerical data will be essential to develop suitably resummed expressions of PN-analytical fluxes in order to improve their accuracy in the strong-field regime.

We set up a field theory model to describe the longitudinal low-energy modes in high density matter present in white dwarf stars. At the relevant scales, ions—the nuclei of oxygen, carbon, and helium—are treated as heavy pointlike spin-0 charged particles in an effective field theory approach, while the electron dynamics is described by the Dirac Lagrangian at the one-loop level. We show that there always exists a longitudinal gapless mode in the system irrespective of whether the ions are in a plasma, crystal, or quantum liquid state. For certain values of the parameters, the gapless mode can be interpreted as a zero sound mode and, for other values, as an ion acoustic wave; we show that the zero sound and ion acoustic wave are complementary to each other. We discuss possible physical consequences of these modes for properties of white dwarfs.

A cosmological magnetic field affects the time evolution of the cosmic matter density field. The squared Alfven velocity of the cosmic fluid is proportional to an ensemble average energy density of a primordial magnetic field (PMF), and it prevents the matter density field from collapsing in the horizon scale. The matter-radiation equality time also is delayed by the presence of the ensemble average energy density of the PMF. The ensemble average energy density of the PMF also affects the matter power spectrum (MPS) through the Meszaros effect and the potential decay. Since the ensemble average energy density of the PMF is not a first order perturbation but a zero order source in the linear perturbation equations for the cosmology, to correctly understand the overall effect of the PMF on the MPS, we should significantly revise previous approaches to research for the MPS with the PMF by considering both the effects of the zero and first order sources from the PMF in the linear perturbation theory. We apply the effects of the zero order sources from the PMF to theoretical computations of the MPS for the first time. We also analyze the overall PMF effect on the MPS. The CMB polarization is affected by the weak lensing. The weak lensing is determined by the MPS. Therefore, we have to consider the zero order sources of the PMF to gain a correct understanding not only of the MPS but also the CMB polarization.

The next galactic core-collapse supernova (CCSN) has already exploded, and its electromagnetic (EM) waves, neutrinos, and gravitational waves (GWs) may arrive at any moment. We present an extensive study on the potential sensitivity of prospective detection scenarios for GWs from CCSNe within 5 Mpc, using realistic noise at the predicted sensitivity of the Advanced LIGO and Advanced Virgo detectors for 2015, 2017, and 2019. We quantify the detectability of GWs from CCSNe within the Milky Way and Large Magellanic Cloud, for which there will be an observed neutrino burst. We also consider extreme GW emission scenarios for more distant CCSNe with an associated EM signature. We find that a three-detector network at design sensitivity will be able to detect neutrino-driven CCSN explosions out to $\sim 5.5\mathrm{kpc}$, while rapidly rotating core collapse will be detectable out to the Large Magellanic Cloud at 50 kpc. Of the phenomenological models for extreme GW emission scenarios considered in this study, such as long-lived bar-mode instabilities and disk fragmentation instabilities, all models considered will be detectable out to M31 at 0.77 Mpc, while the most extreme models will be detectable out to M82 at 3.52 Mpc and beyond.

In this paper we first demonstrate step by step that the factorization hypothesis is valid at the next-to-leading order (NLO) for the exclusive process $\rho {\gamma }^{\star }\to \rho$ by employing the collinear factorization approach, and then extend this proof to the case of the $k_{\mathrm{T}}$ factorization by taking into account the transversal momentum of the light external quark (antiquark) lines in the $\rho$ meson. At the NLO level, we then show that the soft divergences from different subdiagrams will cancel each other in the quark level, while the remaining collinear divergences can be absorbed into the NLO meson wave functions. The full NLO amplitudes can therefore be factorized as the convolution of the NLO wave functions ${\mathrm{\Phi }}_{\rho }^{(1)}$ and the infrared-finite leading order (LO) hard kernels $G_{X,IJ,kl}^0$ in the $k_{\mathrm{T}}$ factorization. We also write down the polarized NLO $\rho$ meson wave functions in the form of nonlocal hadron matrix elements with the gauge factor integral path deviating from the light cone. These NLO $\rho$ meson wave functions can be used to calculate the NLO hard corrections to some relevant exclusive processes, such as $B\to \rho$ transition.

We consider the $O(N+1)/O(N)$ nonlinear sigma model for large $N$ as an effective theory for low-energy QCD at finite temperature $T$, in the chiral limit. At $T=0$ this formulation provides a good description of scattering data in the scalar channel and dynamically generates the $f_0(500)$ pole, the pole position lying within experimental determinations. Previous $T=0$ results with this model are updated using newer analysis of pion scattering data. We calculate the pion scattering amplitude at finite $T$ and show that it exactly satisfies thermal unitarity, which had been assumed but not formally proven in previous works. We discuss the main differences with the $T=0$ result, and we show that one can define a proper renormalization scheme with $T=0$ counterterms such that the renormalized amplitude can be chosen to depend only on a few parameters. Next, we analyze the behavior of the $f_0(500)$ pole at finite $T$, which is consistent with chiral symmetry restoration when the scalar susceptibility is saturated by the $f_0(500)$ state, in a second-order transition scenario and in accordance with lattice and theoretical analysis.

Observation of nonzero neutrino masses at a scale $\sim 10^{-1}–10^{-2}\mathrm{eV}$ is a major problem in the otherwise highly successful Standard Model. The most elegant mechanism to explain such tiny neutrino masses is the seesaw mechanism with right-handed neutrinos. However, the required seesaw scale is so high, $\sim {10}^{14}\mathrm{GeV}$, it will not have any collider implications. Recently, an explicit model has been constructed to realize the seesaw mechanism with the right-handed neutrinos at the electroweak scale. The model has a mirror symmetry, having both the left and right lepton and quark doublets and singlets for the same $SU(2{)}_W$ gauge symmetry. Additional Higgs multiplets have been introduced to realize this scenario. It turns out that these extra Higgs fields also help to satisfy the precision electroweak tests, and other observables. Because the scale of the symmetry breaking is electroweak, both the mirror quark and the mirror leptons have masses in the electroweak scale in the range $\sim 150–800\mathrm{GeV}$. The mirror quarks/leptons decay to ordinary quarks/leptons plus very light neutral scalars. In this work, we calculate the final-state signals arising from the pair productions of these mirror quarks and their subsequent decays. We find that these signals are well observable over the Standard Model background for the 13 TeV LHC. Depending on the associated Yukawa couplings, these decays can also give rise to displaced vertices with long decay lengths, very different from the usual displaced vertices associated with b decays.

A light scalar $\varphi$ with mass $\lesssim 1\mathrm{GeV}$ and muonic coupling $\mathcal{O}(10^{-3})$ would explain the $3.5\sigma$ discrepancy between the Standard Model (SM) muon $g-2$ prediction and experiment. Such a scalar can be associated with a light remnant of the Higgs mechanism in the “dark” sector. We suggest $\varphi \to l^{+}{l}^{-}$ bump hunting in $\mu \to e\nu \overline{\nu }\varphi$, ${\mu }^{-}p\to {\nu }_{\mu }n\varphi$ (muon capture), and $K^{\pm }\to {\mu }^{\pm }\nu \varphi$ decays as direct probes of this scenario. In a general setup, a potentially observable muon electric dipole moment $\lesssim {10}^{-23}e\mathrm{cm}$ and lepton-flavor-violating decays $\tau \to \mu (e)\varphi$ or $\mu \to e\varphi$ can also arise. Depending on parameters, a deviation in BR($H\to {\mu }^{+}{\mu }^{-}$) from SM expectations, due to Higgs coupling misalignment, can result. We illustrate how the requisite interactions can be mediated by weak-scale vector-like leptons that typically lie within the reach of future LHC measurements.